Method for obtaining an air product, and air separation plant

ABSTRACT

An air product is produced in an air separation plant having a heat exchanger, an expansion/compression unit, a rectification unit, liquid storage, cold storage and an air compressor. The air supplied to the rectification unit is conducted through the main air compressor at a pressure level at least 3 bar above the highest operation pressure for the rectification unit. Cryogenic liquids are produced in a first production amount by a first operating mode, a lower second production amount by a second operating mode and a higher third production amount by a third operating mode. Cryogenic liquid is stored in the liquid storage in the third operating mode and removed from storage in the second operating mode. Cryogenic liquid is evaporated in different amounts in each operating mode, which amounts differ by no more than 10%.

The invention relates to a method for obtaining an air product in an air separation plant, and to a corresponding air separation plant.

PRIOR ART

The production of air products in a liquid or gaseous state by cryogenic separation of air in air separation plants is known, and is described for example by H.-W. Häring (Ed.) in Industrial Gases Processing, Wiley-VCH, 2006, in particular section 2.2.5. “Cryogenic Rectification”. The present invention is particularly suitable for air separation plants with internal compression, as explained loc. cit., section 2.2.5.2, “Internal Compression”.

Air separation plants have distillation column systems, which may be designed for example as two-column systems, in particular as classic Linde double-column systems, but also as three- or multi-column systems. Apart from the distillation columns for producing nitrogen and/or oxygen in a liquid and/or gaseous state (for example liquid oxygen, LOX, gaseous oxygen, GOX, liquid nitrogen, LIN and/or gaseous nitrogen, GAN), that is to say the distillation columns for nitrogen-oxygen separation, distillation columns for producing further air components, in particular of the noble gases krypton, xenon and/or argon, may be provided.

For example, it is known from DE 31 39 567 A1 and EP 1 989 400 A1 to use liquid air or liquid nitrogen for grid control and provision of control capacity in electric power grids. At times of a high electricity supply (referred to hereinafter as times when there is a surplus of electric power), the liquid air or the liquid nitrogen is produced in an air separation plant with an integrated liquefier or in a dedicated liquefaction plant and stored in a system of tanks comprising low-temperature tanks. At times of a low electricity supply (referred to hereinafter as times when there is a shortage of electric power), the liquid air or the liquid nitrogen is removed from the system of tanks, the pressure is increased by means of a pump and it is heated to approximately ambient temperature or above, and is thereby transformed into a gaseous or supercritical state. In an energy storage unit, a pressurized stream thereby obtained is expanded to ambient pressure in an expansion turbine or a number of expansion turbines with intermediate heating. The mechanical power thereby released is transformed into electrical energy in one or more generators of the power generating unit and is fed into an electric grid.

U.S. Pat. No. 6,134,916 A discloses a combined system comprising a combined process with integrated gasification, and an air separation unit which outputs oxygen to a gasifier of the combination process with integrated gasification, and a storage unit which stores oxygen until said oxygen is consumed. U.S. Pat. No. 2,788,646 A discloses an air separation method and a corresponding plant with oxygen storage. U.S. Pat. No. 6,134,916 A and U.S. Pat. No. 2,788,646 A seek in each case to provide methods in which a fluctuating demand of consumers can be satisfied with a constant production amount of the air separation plant. U.S. Pat. No. 3,319,434 A and U.S. Pat. No. 2,741,094 A discloses the use of generators in conjunction with temporary oxygen storage.

The present invention is not so much concerned with the area of simply storing energy, but rather seeks to provide an energy separation plant in which air products, in particular internally compressed pressurized nitrogen and/or pressurized oxygen, can be provided, advantageously in comparable amounts, both in times when there is a surplus of electric power and in times when there is a shortage of electric power. At the same time, however, it is sought to utilize the relatively low electricity prices in the times when there is a surplus of electric power, and to avoid relatively high electricity prices in the times when there is a shortage of electric power.

DISCLOSURE OF THE INVENTION

This object is achieved by a process for obtaining an air product in an air separation plant and a corresponding air separation plant having the features described herein.

Before the discussion of the features and advantages of the present invention, the principles on which it is based and the terms used will be discussed.

The discussed devices are also described in the relevant specialist literature, for example loc. cit., section 2.2.5.6, “Apparatus”. Unless the following definitions use different terms, reference is expressly made to the specialist literature for the terminology that is used here.

A “heat exchanger” serves for the indirect transfer of heat between at least two fluid streams which are conducted, for example, in a counterflow configuration with respect to one another, for example a hot compressed-air stream and one or more cold fluid streams or a cryogenic liquid air product and one or more hot fluid streams. A heat exchanger may be formed by a single or multiple heat exchanger sections that are connected in parallel and/or in series, for example one or more plate heat exchanger blocks. It may for example be a plate-type heat exchanger (plate fin heat exchanger). Such a heat exchanger, for example also the “main heat exchanger” of an air separation plant, by which at least the main fraction of the fluid streams to be cooled or heated is cooled or heated, has “passages”, which passages are in the form of mutually separate fluid channels which have heat exchanging surfaces and which are interconnected in parallel and separately by other passages to form “groups of passages”. A characteristic of a heat exchanger is that, in it, at a point in time, heat is exchanged between two mobile media, specifically at least one fluid stream to be cooled and at least one fluid stream to be heated. In this, there is a major difference in relation to a cold storage unit, as will be discussed below, in which an exchange of heat always takes place between one or more mobile media and one or more static media.

A “cold storage unit” serves for storing the thermal energy in the form of cold, that is to say extracted heat energy. For use in the context of the present invention, cold storage units may be structurally designed in particular in a way similar to the regenerators that are known in principle from the area of air separation plants. As discussed in detail below, the operation thereof however differs fundamentally from that of regenerators.

Regenerators are discussed for example in F. G. Kerry, industrial Gas Handbook, CRC Press, 2006, in particular sections 2.7, “Kapitza Cycle” and 4.4.3, “Recovery of Krypton and Xenon”. Regenerators comprise a material that is suitable for storing cold, in the simplest case for example a stone filling, which during a first time period is flowed through by a cold fluid, in particular a cryogenic fluid, and thereby cools down. During a second time period, a corresponding regenerator is flowed through by a hot fluid, which cools down on account of the cold stored in the regenerator or transfers its heat to the regenerator. Regenerators may also be used in air separation plants for cleaning the air that is used particularly of carbon dioxide and hydrocarbons that freeze or liquefy in the cooled regenerator and are vaporized or sublimated during the heating up of the regenerator. In a separation plants of a classic type, corresponding regenerators are typically operated in an alternating mode, in each case with a first generator or first group of generators being regenerated and a second regenerator or a second group of regenerators being on standby for cooling or purifying the feed air.

As mentioned, cold storage units for use in the context of the present invention may duly be of a similar structural design to the known regenerators, though in terms of process engineering, the differences are great. Said differences between cold storage units and regenerators will be discussed below.

A regenerator has primarily the function of a heat exchanger, that is to say it serves for transferring the heat from a relatively hot fluid stream to a relatively cold fluid stream; by contrast to a heat exchanger, it is however the case here that the cold is temporarily stored in a static medium. In an air separation process, therefore, at least two regenerators are always required. The relatively hot stream is conducted through one of the regenerators and the relatively cold fluid stream is conducted through the other. In terms of process engineering, a regenerator pair of said type may basically be replaced by a single conventional heat exchanger in which said fluid streams perform an exchange of heat. If regenerators are taken out of operation without being replaced, the air separation plant is basically no longer functional.

By contrast, the main function of a cold store is that of storing the cold for a relatively long time, for example of more than 30 minutes. In principle, a cold store cannot be replaced by a heat exchanger, because the main purpose of a cold store is to store the cold for extraction at a later point in time, whereas a heat exchanger transfers heat or cold between two mobile media at all times. A cold store is generally used as a single cold store. If the cold store is not in operation, the air separation plant can in principle continue to run without disruption.

A regenerator has in principle only two operating phases. Firstly, a cold or cryogenic fluid stream is conducted through the regenerator and, here, is heated (the regenerator is cooled), generally for less than ten minutes. Thereafter, the regenerator is flowed through in the opposite direction by a hot fluid stream, which is cooled in the process (the regenerator heats up), generally for less than ten minutes.

By contrast, a cold store has at least three operating phases. In a putting-into-storage phase, the cold store is firstly cooled by way of a cold or cryogenic fluid stream; this generally takes longer than one hour. Subsequently, the cold store remains cold during a storage phase of a relatively long period, and is not flowed through. In a removing-from-storage phase, the cold store is then flowed through and heated by a hot fluid stream (in the process, the fluid stream is cooled); this generally takes longer than one hour. This may be followed again by a rest phase, which may also last several hours and in which the cold store is not flowed through.

Other thermodynamic parameters are also different. The average local temperature change in a regenerator amounts to less than 10 K; by contrast, a cold store is, in the interior, heated or cooled on average by approximately 50 K, but at least by 30 K.

An “expansion turbine” or “expansion machine”, which may be coupled to further expansion turbines or energy converters such as oil brakes, generators or compressors by way of a common shaft, is designed for the expansion of a gaseous or at least partially liquid stream. In particular, for use in the present invention, expansion turbines may be designed as turbo expanders. If a compressor is driven by one or more expansion turbines, but without energy that is externally supplied, for example by means of an electric motor, the term “turbine-driven” compressor or alternatively “booster” is used. Arrangements comprising turbine-driven compressors and expansion turbines are also referred to as “booster turbines”.

An “air product” is any product that can be produced at least by compressing and cooling air and in particular, but not necessarily, by subsequent cryogenic rectification. In particular, it may be liquid or gaseous oxygen (LOX, GOX), liquid or gaseous nitrogen (LIN, GAN), liquid or gaseous argon (LAR, GAR), liquid or gaseous xenon, liquid or gaseous krypton, liquid or gaseous neon, liquid or gaseous helium, etc., or else for example liquid air (LAIR). The terms “oxygen”, “nitrogen” etc. also refer here respectively to cryogenic liquids or gases which comprise the respectively mentioned air component in an amount that lies above that of atmospheric air. Therefore, they do not necessarily have to be pure liquids or gases with high contents.

In the context of the present application, an “air product” is also understood as meaning a corresponding fluid that is finally discharged from the air separation plant, that is to say is no longer used for expansion, evaporation, liquefaction, compression etc. in the air separation plant or subjected to a corresponding step. Fluids produced by compressing and cooling air, and in particular, but not necessarily, by subsequent cryogenic rectification, which fluids are only intermediately stored or temporarily available but are subsequently further treated in the air separation plant, are not referred to here as air products. An example of this is in particular a cryogenic liquid produced from air, which cryogenic liquid is however not discharged as an air product from the air separation plant but is pressurized in liquid form as part of an internal compression process and is subsequently heated in the main heat exchanger of an air separation plant. It is thus there that the air product itself is formed for the first time.

As mentioned in the introduction, air separation plants may be operated with so-called internal compression. With regard to details, reference is made to the cited specialist literature. In the internal compression, a stream pressurized in liquid form is heated and is thereby transformed from the liquid to the gaseous or supercritical state depending on the level to which the liquid fluid stream has been pressurized. For the transformation from the liquid to the gaseous state, the expression “evaporation” is hereinafter also used, and for the transformation from the liquid to the supercritical state, the expression “pseudo-evaporation” is also used.

In the air separation, use may in principle be made of methods in which all of the feed air, that is to say all of the air that is fed into the distillation column system, is firstly brought approximately to the pressure of the high-pressure column by way of a main air compressor (MAC), and only a part thereof is subsequently recompressed to a relatively high pressure by way of a booster air compressor (BAC). These rather conventional methods are also referred to as MAC/BAC methods. MAC/BAC methods are described in detail for example in the specialist literature cited in the introduction.

In a MAC/BAC method, a considerable part of the so-called feed air conducted through the main air compressor (in general more than 30% of said feed air) is fed at typically approximately 5.2 to 9 bar, in particular at approximately 5.6 bar, into the high-pressure column of a dual-column system, and, beforehand, is cooled in the main heat exchanger of the air separation plant from approximately ambient temperature or higher to typically approximately −160 to −170° C. Said fraction is, beforehand, only compressed by the main air compressor to the stated pressure, and typically does not undergo recompression. A second part of the total feed air conducted through the main air compressor, the so-called throttle stream, is, by contrast, in a MAC/BAC process, compressed in the booster air compressor from the abovementioned pressure of the main air compressor to a considerably higher pressure, generally supercritical pressure, and is likewise cooled in the main heat exchanger of the air separation plant from approximately ambient temperature or higher to typically approximately −160 to −170° C. A third air stream, the so-called turbine stream, which cools in the main heat exchanger only to an intermediate temperature of approximately −100 to −150° C. and is subsequently expanded in an expansion machine, can, in known MAC/BAC processes, be provided both by the main air compressor and by the booster air compressor (via a suitable outlet or a corresponding intermediate extraction point).

Recently, instead of the MAC/BAC processes, use has increasingly been made of so-called HAP (high air pressure) processes, because these can offer advantages in relation to the MAC/BAC processes in certain usage scenarios. In an HAP process, all of the feed air is compressed in the main air compressor to a pressure considerably higher than the pressure in the high-pressure column or than the highest operating pressure in the rectification unit that is used. The pressure difference that is used amounts in this case to at least 3 bar, though may also be considerably higher, for example maybe 4, 5, 6, 7, 8, 9 or 10 bar, and may for example be up to 14, 16, 18 or 20 bar. HAP process are known for example from EP 2 466 236 A1, from EP 2 458 311 A1, and from U.S. Pat. No. 5,329,776 A.

In an HAP method, the air, which corresponds to the air described above which, in an MAC/BAC process, is fed into the high-pressure column and, beforehand, is cooled in the main heat exchanger of the air separation plant from approximately ambient temperature or higher to typically approximately −160 to −170° C., is not treated in this way. Said air is extracted not from the main heat exchanger but rather from the outlet of one or more expansion machines in which said air is expanded from the considerably higher pressure level of the main air compressor and, in this way, cooled for the first time to typically approximately −160 to −170° C. Said air is also referred to as “feed air”. In the HAP process, too, a throttle stream is used; however, by contrast to an MAC/BAC process, said throttle stream does not necessarily need to be compressed in a compressor driven using externally provided energy. The throttle stream, or else multiple throttle streams, may in this case also merely be recompressed by way of one or more boosters, which may be driven for example by the one or more expansion machines mentioned above. A separate turbine stream does not have to be provided.

ADVANTAGES OF THE INVENTION

The present invention proposes a method for producing an air product in an air separation plant having a heat exchanger unit, having an expansion/compression unit, having a rectification unit, having a liquid storage unit, having a cold storage unit and having a main air compressor. The heat exchanger unit of the air separation plant according to the invention comprises at least one heat exchanger, in particular the known heat exchanger such as encountered in conventional air separation plants. A main heat exchanger of said type may also be in the form of multiple separate heat exchanger units or heat exchanger blocks.

The expansion/compression unit serves for partially expanding, and partially recompressing, the feed air supplied to the air separation plant and compressed in the main air compressor, in order to thereby provide compressed-air streams at different pressure levels. A corresponding expansion/compression unit may thr this purpose have respectively suitable expansion turbines and compressors, which may in particular also be coupled to one another. It is thus possible for turbine-driven compressors or booster turbines as discussed above to be provided. It is also possible, for example, for generator turbines to be used, but in particular no compressor is driven by external energy. With regard to details, reference is made to the appended FIGS. 1 and 2, which discuss further aspects of corresponding expansion/compression units.

The rectification unit of the air separation plant used according to the invention may in particular have a classic Linde dual column with a high-pressure column and a low-pressure column, with or without argon production or with or without separation of krypton and xenon, and with or without separation of helium and neon. Other configurations are however also possible. The liquid storage unit of the air separation plant used according to the invention comprises in particular one or more liquid tanks, which are in particular temperature-insulated and/or arranged in a suitable cold box, for cryogenic air products such as have been discussed above. Said liquid tanks will hereinafter be referred to as “liquid air stores”, “liquid nitrogen stores”, etc. The main air compressor may in particular comprise multiple compression stages and be in the form of a radial compressor.

In the context of the present invention, all of the air supply to the rectification unit, that is to say all of the feed air, is conducted through the main air compressor and, there, is firstly compressed to a pressure level which lies at least 3 bar above the highest pressure level at which the rectification unit is operated. Said highest pressure level is typically the operating pressure of the high-pressure column, if a dual-column system is used. The air separation process is thus configured as an HAP process, as has been discussed above. The pressure difference may also be even greater, for example may assume the values mentioned in detail above.

Aside from the compression in the main air compressor, the method advantageously comprises no further compression of the feed air, or of any part thereof, in a compressor driven using external energy. If a partial further compression of the feed air is performed, this is, in other words, performed always and exclusively by way of turbine-driven compressors as discussed above.

One or more cryogenic liquids is or are produced, specifically in a first production amount in a first operating mode, in a second production amount in a second operating mode and in a third production amount in a third operating mode, in the air separation plant according to the present invention using the correspondingly highly compressed air or feed air conducted through the main air compressor. The amount of the cryogenic liquids thrilled correlates closely with the energy consumption of the air separation plant. According to the invention, the second production amount is in this case lower than the first production amount, and the third production amount is higher than the first production amount.

Where different “operating modes” are referred to here and below, the “second operating mode” is to be understood to mean the operating mode that is implemented in times when there is a shortage of electric power. Correspondingly, the “third operating mode” is to be understood to mean the operating mode that is implemented in times when there is a surplus of electric power. Because, as mentioned, the second production amount of the cryogenic liquid(s) is advantageously lower than the first production amount, and the third production amount is higher than the first production amount, it is a case in the context of the invention that considerably less energy is consumed in the second operating mode than in the third and in the first operating mode. By contrast, the energy consumption in the third operating mode is higher than in both of the other operating modes. In this way, by way of the method according to the invention, the availability of electric power can be efficiently utilized in each case, while avoiding high costs. By contrast, the “first operating mode” is comparable to the operation of an air separation plant without a liquid storage unit.

In order to be able to provide the same or similar amounts of air products in all operating modes, the liquid storage unit is used. Here, the one or more cryogenic liquids is or are stored in the liquid storage unit in a putting-into-storage amount, which corresponds to a partial amount of the third production amount, in the third operating mode, and said one or more cryogenic liquids is or are removed from storage in the liquid storage unit, in a removing-from-storage amount, in the second operating mode. In other words, the “surplus” cryogenic liquid produced in the third production amount in the third operating mode is temporarily stored in the liquid storage unit, in order for it to be able to be extracted again in the second operating mode and utilized for the compensation of the in this case relatively low liquid production in the form of the second production amount. By contrast, the first operating mode is distinguished in particular by the fact cryogenic liquids are neither put into storage in the liquid storage unit nor removed from the liquid storage unit.

The one or more cryogenic liquids is or are evaporated and/or pseudo-evaporated in a first evaporation amount in the first operating mode, in a second evaporation amount in the second operating mode and in a third evaporation amount in the third operating mode, wherein the first evaporation amount corresponds to the first production amount, the second evaporation amount corresponds to the second production amount plus the removing-from-storage amount, and the third evaporation amount corresponds to the third production amount minus the putting-into-storage amount. In other words, the relatively low production amount in the second operating mode is compensated by way of the removing-from-storage amount. The first, second and third evaporation amounts correspond to one another, or at least of similar magnitude, that is to say, according to the invention, differ from one another by no more than 10%, 5% or 1%. In this way, it is possible, regardless of production amounts consuming different amounts of energy, for a similar amount of (internally compressed) air products to be provided at all times.

For the temporary storage of the cold which is released in the second operating mode as a result of the extraction of the cryogenic liquid(s) from the liquid storage unit and the evaporation thereof, and which is thus available in surplus, and for the provision of cold which is additionally required in the third operating mode for the provision of the cryogenic liquid(s) to be put into storage in the liquid storage unit, a cold storage unit of the type discussed above is used. For the exchange of heat with said cold storage unit, use is made of cryogenic and hot fluid streams. According to the invention, it is provided for this purpose that, likewise using the air conducted through the main air compressor, in the second operating mode, a cryogenic fluid stream is formed, using which the cold storage unit is cooled and which is thereby heated, and in the third operating mode, a hot fluid stream is formed, using which the cold storage unit is heated and which is thereby cooled. By contrast, in the first operating mode, the cold storage unit is advantageously not flowed through by corresponding fluid streams. Examples of such fluid streams will also be discussed below with reference to the appended figures.

A “cryogenic” fluid stream is present in particular at a temperature level of considerably below −100° C., for example at −160 to −170° C. By contrast, a “hot” fluid stream is present for example at a temperature level which corresponds at least to the ambient temperature, or for example at least to 0° C. The temperature level thereof lies in any case above that of the cryogenic fluid stream. By way of the discussed measures, it is possible for the cold that is released during the evaporation of the one or more cryogenic liquids to be stored in the second operating mode. Said cold is thus available for the third operating mode, in which it is sought for additional cryogenic liquids to be produced and stored in the liquid storage unit.

The method according to the invention, which as already discussed is used in an HAP process, comprises in particular, as is common in an HAP process of said type, that a part of the air conducted through the main air compressor and compressed there is expanded to a pressure level which corresponds at least to the highest pressure level at which the rectification unit is operated. Here, the air may be expanded to a pressure slightly higher than said highest pressure level, for example to a pressure level which lies at least 1 bar above said highest pressure level, such that said air can be fed into the high-pressure column of the rectification unit without further delivery measures. For such an expansion, it is the case in particular, as already discussed, that expansion turbines are provided. By way of the expansion therein, the expanded air cools for example to −160 to −170° C., even though it has not previously been cooled to this extent in the heat exchanger unit.

It is advantageously possible here for the cryogenic fluid stream and the hot fluid stream that are conducted through the cold storage unit in the third and/or second operating mode to be formed from a part of said expanded air. To provide the cryogenic fluid stream and the hot fluid stream at the different temperature levels, and in this way permit the cold storage proposed according to the invention, a part of said expanded air may, to form the cryogenic fluid stream, be used unheated as the cryogenic fluid stream after the expansion. To form the hot fluid stream, a corresponding part of said expanded air is, by contrast, heated in the heat exchanger unit. After the heating of the cryogenic fluid stream in the cold storage unit, whereby the cold storage unit is cooled, said fluid stream is advantageously cooled again to a temperature level at which it can be fed into the rectification unit, for example to a temperature level of −160 to −170° C. This yields an advantageous coupling or exchange of heat between the heat exchanger unit, or a main heat exchanger used therein, and the cold storage unit, or cold storage means used here.

In the second operating mode, in which the one or more cryogenic liquids are removed from storage in the liquid storage unit, it is in principle the case, owing to the typically lower production amounts of cryogenic liquid in the rectification unit, that a lower amount of cold is required for the operation of the air separation plant, or an additional cooling amount is available here. Said amount of cold may, as already discussed, be utilized by virtue of a part of the air that is cooled to the said temperature level of typically −160 to −170° C. as a result of the expansion being conducted through the cold storage unit and cooling the latter. As mentioned, the air is heated up in the process, and can subsequently be cooled by cooling in the main heat exchanger of the heat exchanger unit, such that the corresponding air is ultimately also, after being conducted through the cold storage unit and undergoing the heating that takes place therein, present at a suitable temperature level for being fed into the rectification unit, specifically at said temperature level of −160 to −170° C. again. Said air can thus be fed, together with the expanded air not used for forming the cryogenic fluid stream, into the rectification unit or into the high-pressure column thereof. Conversely, as mentioned, in the third operating mode, in which additional cryogenic liquid is produced and fed into the liquid storage unit, that is to say the production amount is relatively high, an additional cooling demand exists. Said demand is covered by virtue of the fact that the air expanded as discussed above is firstly heated in the main heat exchanger or in the heat exchanger unit, such that corresponding cold is available for cooling other streams. The cold that is “lost” in this way can subsequently be transferred, in the cold unit, to the heated part of the air again. After passing through the cold storage unit, said air is therefore again present at the temperature level suitable for feeding into the high-pressure column, of −160 to −170° C. The formation of the cryogenic fluid stream and of the hot fluid stream from the expanded air will be discussed in more detail with reference to the appended FIGS. 3A to 3C and 4A to 4C.

As an alternative to this, the cryogenic fluid stream may however also be formed from a part of the one or more cryogenic liquids that is or are evaporated or pseudo-evaporated in the second operating mode, before the evaporation thereof. By contrast, the hot fluid stream may be formed from a part of the one or more cryogenic liquids that is or are evaporated or pseudo-evaporated in the third operating mode, after the evaporation thereof. Here, in the second operating mode, a part of the cryogenic liquid to be evaporated is conducted not through the main heat exchanger but through the cold storage unit. Because additional cold is available owing to the evaporation of the additional cryogenic liquid from the liquid storage unit, said cold can be stored in the cold storage unit without losses arising in the main heat exchanger or in a main heat exchanger unit. The cold that is available in the main heat exchanger therefore does not change. Conversely, in the third operating mode, the hot fluid stream may, as mentioned, be formed, after the evaporation of a corresponding cryogenic liquid, from a part of said then evaporated cryogenic liquid. In this way, it is for example also possible for a liquefaction product to be generated again directly from a corresponding fluid stream and put into storage in the liquid storage unit. This is correspondingly discussed with reference to FIGS. 5A to 5C.

Alternatively or in addition, so-called impure nitrogen may be used for providing the corresponding cryogenic and hot fluid streams. Corresponding impure nitrogen constitutes a gas mixture which is extracted from a low-pressure column of a rectification unit with a high-pressure column and a low-pressure column, and which comprises a nitrogen content of typically approximately 0.5 to 5 mole percent. Such impure nitrogen may, similarly to the fluid streams discussed above, be used for forming the cryogenic fluid stream and the hot fluid stream. In particular, such impure nitrogen may, in the second operating mode, be conducted unheated through the cold storage unit to form the cryogenic fluid stream, whereas in the third operating mode, a corresponding fluid stream is heated, and is in particular conducted through a corresponding unit by way of a blower. In other words, the cryogenic fluid stream and the hot fluid stream may be formed from a part of the gas mixture extracted from the low-pressure column in the form of the impure nitrogen, wherein said part is used unheated to form the cryogenic fluid stream and is heated in the heat exchanger unit to form the hot fluid stream. The use of impure nitrogen in the manner discussed is shown in FIGS. 6A to 6C, 7A to 7C and 8A to 8C.

In the case of corresponding impure nitrogen being used, it is in particular also possible for use to be made of a main heat exchanger with a further heat exchanger passage, such that a part of the hot fluid stream, after being cooled in the cold storage unit, can be heated in the heat exchanger unit, and can hereby transmit its cold to the other fluids in the heat exchanger unit. This is shown in the appended FIGS. 8A to 8C.

Instead of the air that is expanded and fed into the high-pressure column, it is also possible in the context of an embodiment of the invention for a further compressed-air stream, specifically the throttle stream mentioned in the introduction, to be used for cooling the cold storage unit. It is thus possible for a further part of the air that is conducted through the main air compressor and compressed there to be compressed further and cooled in the heat exchanger unit. Corresponding air is typically, in known plants, subsequently expanded, as discussed with reference to FIG. 1, and fed into the high-pressure column. The cryogenic fluid stream and the hot fluid stream may in this case be formed from a part of the further compressed air that is cooled in the heat exchanger unit, wherein said part is used unheated to form the cryogenic fluid stream and is heated in the heat exchanger unit to form the hot fluid stream. This is also discussed in more detail with reference to FIGS. 9A to 9C.

The cold storage unit advantageously comprises first cold storage means and second cold storage means, wherein in each case a first part of the cryogenic fluid stream and of the hot fluid stream is conducted through the first cold storage means, and a second part of the cryogenic fluid stream and of the hot fluid stream is conducted through the second cold storage means. In this way, improved balancing of the cold storage unit and of the main heat exchanger can be achieved, in particular if the second part of the hot fluid stream and of the cryogenic fluid stream is conducted in each case through a section of a main heat exchanger of the heat exchanger unit, before and/or after being conducted through the second cold storage means. This is correspondingly illustrated in FIGS. 4A to 4C and 7A to 7C.

In the context of the present invention, any desired cryogenic liquids may be used, for example a nitrogen-rich and/or an argon-rich and/or an oxygen-rich liquid and/or liquid air.

The invention also relates to an air separation plant having the features described herein. With regard to the features and advantages of a corresponding air separation plant, reference is therefore expressly made to the explanations given above.

The invention will be discussed in more detail below, in relation to the prior art, with reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, in the form of a schematic flow diagram, an air separation plant that does not conform to the invention.

FIG. 2 shows, in the form of a schematic flow diagram and in a partial view, an air separation plant that does not conform to the invention.

FIGS. 3A to 3C show, in the form of schematic flow diagrams, an air separation plant according to an embodiment of the invention in three operating states.

FIGS. 4A to 4C show, in the form of schematic flow diagrams, an air separation plant according to an embodiment of the invention in three operating states.

FIGS. 5A to 5C show, in the form of schematic flow diagrams, an air separation plant according to an embodiment of the invention in three operating states.

FIGS. 6A to 6C show, in the form of schematic flow diagrams, an air separation plant according to an embodiment of the invention in three operating states.

FIGS. 7A to 7C show, in the form of schematic flow diagrams, an air separation plant according to an embodiment of the invention in three operating states.

FIGS. 8A to 8C show, in the form of schematic flow diagrams, an air separation plant according to an embodiment of the invention in three operating states.

FIGS. 9A to 9C show, in the form of schematic flow diagrams; an air separation plant according to an embodiment of the invention in three operating states.

DETAILED DESCRIPTION OF THE DRAWINGS

In the figures, elements which correspond to one another are denoted by identical reference designations and, for the sake of clarity, will not be discussed more than once. Fluid streams are additionally denoted by triangular flow arrows, wherein filled (black) flow arrows denote fluid streams in a liquid state, and non-filled (white) flow arrows denote fluid streams in a gaseous state.

FIG. 1 illustrates, in the form of a simplified schematic flow diagram, an air separation plant which does not conform to the invention. The air separation plant comprises a main heat exchanger unit 10, an expansion/compression unit 20, a rectification unit 30 and a liquid storage unit 40, which are illustrated separately merely for the sake of clarity. In particular, the main heat exchanger unit 10 and the expansion/compression unit 20 may in practice exhibit a high level of structural integration, and may for example be arranged in a common cold box.

The main heat exchanger unit 10 comprises, as central component, a main heat exchanger 11 which may be in the form of one or more structural units. In the example illustrated here, the expansion/compression unit 20 comprises a first booster turbine 21 and a second booster turbine 22. It is however possible for one or more booster turbines to be replaced with one or more generator turbines, or for combinations of corresponding units to be used. The booster stage(s) of one or more booster turbines or the like may be in the form of (a) conventional booster stage(s) or in the form of (a) so-called “cold” booster stage(s), the inlet temperature of which is lower than the ambient temperature. The expansion/compression unit 20 is thermally coupled to the main heat exchanger unit 10 or to the main heat exchanger 11 thereof.

In the example illustrated, the rectification unit 30 has a dual column formed from a high-pressure column 31 and a low-pressure column 32. The high-pressure column 31 and the low-pressure column 32 are connected in heat-exchanging fashion by way of a main condenser 33. Furthermore, by way of example, a subcooling counterflow means 34, optionally a generator turbine 35, and multiple valves and pumps (not separately designated) are provided. The liquid storage unit 40 comprises for example a liquid nitrogen store 41, a liquid air store 42 and a liquid oxygen store 43, which may in each case be in the form of one or more, in particular insulated, tanks. A further liquid air store 45 which is functionally assigned to the liquid storage unit 40 may be provided.

In the air separation plant shown in FIG. 1, feed air (AIR) is drawn in, in the form of a fluid stream a, by way of a main air compressor 1 illustrated in simplified form, is cooled in a pre-cooling unit 2, and is purified in a purification unit 3. The air separation plant is designed for the implementation of an HAP process; therefore, the main air compressor 1 compresses the air of the fluid stream a that is conducted through it to a correspondingly high, predefined pressure level, which lies considerably above the maximum separation pressure used in the rectification unit 30, that is to say above the operating pressure of the high-pressure column 31, and is in this case at least 9 bar.

The correspondingly compressed, cooled and purified air of the fluid stream a (MPAIR) is supplied to the main heat exchanger unit 10 and to the expansion/compression unit 20. In the main heat exchanger unit 10 and in the expansion and compression unit 20, multiple compressed-air streams at different pressure and temperature levels are generated from the air of the fluid stream a. In FIG. 1, a compressed-air stream b (FEED) for feeding into the rectification unit 30 or the high-pressure column 31 thereof, and further compressed-air streams c and d (JT1-AIR, JT2-AIR) are illustrated. The compressed-air stream b (FEED) is in this case provided at a pressure level of for example approximately 5.6 bar, and is fed into a high-pressure column 31 of the rectification unit 30. The compressed-air stream c (JT1-AIR) is provided at a pressure level which lies above that of the compressed-air stream b (MPAIR). The compressed-air stream d (JT2-AIR) is optionally provided; the pressure level thereof likewise lies above that of the compressed-air stream b (MPAIR). Furthermore, it is optionally possible for a further compressed-air stream (LP-AIR, not shown in FIG. 1) to be provided at a pressure level of for example approximately 1.4 bar, which further compressed-air stream is subsequently conducted, as so-called injection air, into the low-pressure column 32 or through the main heat exchanger 11 into the surroundings. The provision of the compressed-air streams b, c and d is illustrated in highly schematic form in FIG. 1, in particular with regard to the expansion/compression unit 20, and may be realized in different ways. One example for the provision of the compressed-air streams b, c and d is illustrated in FIG. 2.

As mentioned, the compressed-air stream b (FEED) is fed into the high-pressure column 31 of the rectification unit 30. The compressed-air stream c (JT1-AIR) is expanded into the high-pressure column 31 of the rectification unit 30. Here, use may for example be made of the generator turbine 35 that is shown, and optionally of one or more valves (not separately designated). The optionally provided compressed-air stream d (JT2-AIR) is likewise expanded into the high-pressure column 31 of the rectification unit 30, via a valve which is not separately designated.

In the high-pressure column 31 of the rectification unit 30, an oxygen-enriched liquid bottom product is produced which is drawn off in the form of a fluid stream e, is conducted through the subcooling counterflow means 34, and is expanded into the low-pressure column 32 of the rectification unit 30 via a valve which is not separately designated. Furthermore, in the high-pressure column 31 of the rectification unit 30, a nitrogen-enriched gaseous overhead product is produced which is drawn off in the form of a fluid stream f. A part of the fluid stream f may be led out of the air separation plant is a gaseous nitrogen-rich air product (PGAN), and the rest may be liquefied in the main condenser 33.

A part of the liquefaction product that is formed here may be led out of the air separation plant in the form of a liquid nitrogen-rich air product (PLIN), and a part is recycled, as a recycle component, to the high-pressure column 31 of the rectification unit 30. A further part of the liquefaction product may be conducted in the form of the fluid stream g through the subcooling counterflow means 34 and expanded into the low-pressure column 32 of the rectification unit 30 via a valve which is not separately designated. A further part of the liquefaction product may, in the form of the fluid stream h, be pressurized by way of a pump (not separately designated), depending on the operating mode merged with a likewise pressurized, nitrogen-rich liquid fluid stream i from the liquid nitrogen store 41 of the liquid storage unit 40 and/or from the head of the low-pressure column 32, and, as an internally compressed, liquid, nitrogen-rich fluid stream k (ICLIN), in particular in the form of two partial streams, evaporated or pseudo-evaporated in the main heat exchanger 11, and subsequently provided as internally compressed, nitrogen-rich pressure product at different pressure levels (ICGAN1, ICGAN2).

Air that is liquefied during the expansion of the compressed-air stream c and optionally of the compressed-air stream d into the high-pressure column 31 of the rectification unit 30 may be drawn off, in the form of the fluid stream 1, directly below the infeed point of said streams, conducted through the subcooling counterflow means 34, and expanded into the low-pressure column 32 of the rectification unit 30 via a valve which is not separately designated. A part may also be stored in the liquid air store 42 or 45 of the liquid store unit 40. A fluid stream m may be drawn off from the high-pressure column 31, conducted through the subcooling counterflow means 34 and expanded via a valve (not separately designated) into the low-pressure column 32 of the rectification unit 30.

A liquid, oxygen-rich bottom product is formed in the low-pressure column 32, which bottom product is drawn off in the form of a fluid stream n and, depending on the operating mode, fed in the form of a fluid stream o into the liquid oxygen store 43 and/or pressurized by way of one of the pumps (not separately designated) and heated, as an internally compressed, liquid, nitrogen-rich fluid stream p (ICLOX), in the main heat exchanger 11 of the main heat exchanger unit 10, and, in particular in the form of two partial streams, evaporated or pseudo-evaporated in the main heat exchanger 11 and provided as internally compressed, oxygen-rich pressure product at two pressure levels (MP-GOX, HP-GOX). The fluid stream p (ICLOX) may also, depending on the operating mode, be formed using an oxygen-rich liquid extracted from the liquid oxygen store 43 of the liquid storage unit 40. The fluid stream o is therefore illustrated as being bidirectional. It is furthermore possible for corresponding oxygen-rich liquid to also be extracted in the form of the fluid stream q from the liquid oxygen store 43 of the liquid storage unit 40, and fed by way of a pump into the low-pressure column 32.

For the filling of the liquid nitrogen store 41 of the liquid storage unit 40, it is possible tier a nitrogen-rich liquid to be extracted in the form of a fluid stream r from an upper region of the low-pressure column 32 and transferred in the form of a fluid stream s into the liquid nitrogen store 41. The fluid stream s is also illustrated as being bidirectional. Depending on the operating mode, it is also possible for liquid to be extracted in the form of the fluid stream s from the liquid nitrogen store 41 and treated in the form of the fluid stream i as discussed above. Nitrogen-rich liquid may also be fed back, in the form of a fluid stream t, from the liquid nitrogen store 41 of the liquid storage unit 40 into an upper region of the low-pressure column 32. The liquid stores 41, 42 and 43 may be structurally formed as separate structural units or integrated into the rectification columns. In any case, they are functionally part of the liquid storage unit.

A nitrogen-rich fluid stream u drawn off from the head of the low-pressure column 32 may be conducted through the subcooling counterflow means 34, heated in the main heat exchanger 11 and provided as nitrogen product (GAN). A fluid stream v, so-called impure nitrogen (UN2), is treated similarly, and is used as a so-called residual gas (Rest).

The liquid air store 42 may be fed not only with the liquid air of the fluid stream in but also with liquid air from the low-pressure column 32 in the form of the fluid stream w. Correspondingly, liquid air may also be fed back from the liquid air store 42 into the low-pressure column 32 in the form of a fluid stream x by way of a pump.

The air separation plant illustrated in FIG. 1 is distinguished not only by the high-pressure level to which the main air compressor 1 compresses all of the feed air of the fluid stream a but in particular also by the fact that the air that is fed into the distillation column system is provided predominantly using one or more expansion turbines.

FIG. 2 illustrates one possibility for the provision of the compressed-air streams b (FEED) and c (JT-AIR; here, no compressed-air stream corresponding to the fluid stream d as per FIG. 1 is provided) already shown in FIG. 1. The incorporation into the air separation plant shown in FIG. 1 is apparent directly from the designation of the fluid streams; the expansion/compression unit 20 and the main heat exchanger unit 10 are in this case illustrated as a unit 10/20. As mentioned, other possibilities may however also be used.

Here, the fluid stream a is, after the compression, divided into the streams b and c. The partial stream b is supplied to the heat exchanger 11 at the hot side and is extracted at an intermediate temperature level. After a parallel expansion of partial amounts of the partial stream b in the expansion turbines of the booster turbines 21 and 22, said partial amounts are merged again. The fluid stream c is compressed in the compressor stages of the booster turbines 22 and 21. Because the fluid stream c has not been previously cooled, said compressor stages are “hot” compressor stages. FIG. 2 illustrates aftercoolers (not separately designated) which are arranged downstream of the respective compressor stages. The partial stream c is subsequently conducted through the main heat exchanger 11 from the hot to the cold end.

The following FIGS. 3A to 3C to 9A to 9C show in each case partial views of air separation plants according to embodiments of the invention in three operating states, wherein the sub-figures A illustrate in each case the first operating mode, as has been discussed several times, the sub-figures B illustrate in each case the second operating mode, which has been discussed several times, and the sub-figures C illustrate in each case the third operating mode, which has been mentioned several times. The designations of the streams, devices and apparatuses correspond in this case to FIGS. 1 and 2, in each case one main heat exchanger 11, the booster turbines 21 and 22, the rectification unit 30, the liquid storage unit 40 with the liquid nitrogen store 41, the liquid air store 42, the liquid oxygen store 43 and a liquid argon store 44 are shown. Not all of said stores 41 to 44 need to be provided. It is also possible for additional stores to be provided. In the following figures, respectively inactive streams, or lines which are not flowed through by fluids, are illustrated with crosses through them. Furthermore, the figures illustrate a cold storage unit 50 with a first cold storage means 51 and, in some cases, a second cold storage means 52.

FIGS. 3A to 3C show how a part of the air, compressed by way of the main air compressor 1, of the fluid stream b, which is subsequently expanded, can, in one embodiment of the present invention, be used for cold or energy storage and for the recovery thereof.

In the first operating mode, which is illustrated in FIG. 3A, the cold storage unit 40 is in this case not in operation. The air separation plant operates substantially as shown in FIG. 1 in conjunction with FIG. 2. In other words, the fluid stream b is supplied to the hot side of the main heat exchanger 11, is extracted at an intermediate temperature level, is expanded in the expansion turbines of the booster turbines 21 and 22, and is subsequently fed (FEED) entirely into the rectification unit 30. The fluid stream c is compressed by way of the boosters of the booster turbines 21 and 22, is subsequently cooled in the main heat exchanger 11 and (JT-AIR) is fed into the rectification unit 30. With regard to the other streams, reference is made to the explanations given above.

As illustrated by way of a solid arrow in the rectification unit 30, it is the case here that the fluid stream p (ICLOX) is provided exclusively by extraction from the rectification unit 30 or from the low-pressure column 32 thereof (cf. FIG. 1). This correspondingly also applies to other liquid streams.

In the second operating mode illustrated in FIG. 3B, the cold storage unit 50 with the cold storage means 51 thereof is in operation. In the second operating mode, a part of the fluid stream b is branched off therefrom and is conducted, in the form of the fluid stream b1, through the cold storage unit 50 or the cold storage means 51 thereof. Owing to the cooling of the fluid stream b in the main heat exchanger 31 and the expansion thereof in the expansion turbines of the booster turbines 21 and 22, the fluid stream b1 is present at a temperature level of approximately −160 to −170° C. Therefore, said fluid stream b1 can be utilized for cooling the cold storage unit 50 or the cold storage means 51 thereof. Because the fluid stream b1 has been heated in the cold storage unit 50 or the cold storage means 51 thereof, it must be cooled again to set temperature level before being fed into the rectification unit 30 or the high-pressure column 31. Therefore, the fluid stream b1, after being heated in the cold storage unit 50 or the cold storage means 51 thereof, is cooled again to the stated temperature level in the main heat exchanger 11. The fluid stream b1 is, along with that part of the fluid stream b which is not conducted to the cold storage unit 50 or the cold storage means 51 thereof, fed into the rectification unit 30, in particular the high-pressure column 31. The infeed is realized as shown with regard to fluid stream c in FIG. 1; the two partial amounts are, for the sake of better clarity, denoted by FEED1 and FEED2 in FIG. 3B.

The main heat exchanger 11 is capable of performing said additional cooling of the fluid stream b1 in the second operating mode because one or more cryogenic liquids are extracted from the liquid storage unit 40 (cf. also streams t, s, o, q, w and x as per FIG. 1, in this case fluid stream q). As already discussed with reference to FIG. 1, oxygen-rich liquid is extracted from the rectification unit 30 or from the low-pressure column 31 and is, in the form of the fluid stream p (ICLOX), evaporated in the heat exchanger unit 10 or in the main heat exchanger. If a part of said oxygen-rich liquid of the fluid stream p (ICLOX) is now no longer covered by the extraction from the rectification unit 30 or the low-pressure column 31 alone, but rather a part is extracted, for example in the form of the fluid stream q, from the liquid oxygen store 43 of the liquid storage unit 40, a lower amount of cold is required for the provision of the same or a similar amount of the fluid stream p (ICLOX). The cold that is thus provided “in surplus” can be transferred to the fluid stream b1, which has previously transferred its cold into the cold storage unit 50 or the cold storage means 51 thereof.

The liquid extracted from the liquid oxygen store 41 of the liquid storage unit 40 is indicated by way of a dashed arrow within the rectification unit 30, and a part extracted from the low-pressure column 31 is denoted by a solid arrow. It is expressly pointed out that, aside from oxygen, use may also be made of other fluids which can be stored in liquid form in the liquid storage element 40 and correspondingly extracted and evaporated.

In the third operating mode illustrated in FIG. 3C, it is likewise the case that a partial amount of the fluid stream b, in this case denoted by b2, is firstly heated in the main heat exchanger 11 and is subsequently conducted through the cold storage unit 50. The fluid stream b1 is, in the main heat exchanger 11, heated for example from the discussed approximately −160 to −170° C. to a temperature level above 0° C. In this way, an additional amount of cold is available in the main heat exchanger 11. This may be utilized to form a greater amount of the oxygen-rich liquid in the low-pressure column 31. That fraction thereof which is not led out of the plant in the form of the fluid stream p (ICLOX) may be transferred in the form of the fluid stream o into the liquid oxygen store 43 of the liquid storage unit 40. Here, the amount of the fluid stream p (ICLOX) remains the same or similar.

Because the fluid stream b2 has been heated in the main heat exchanger 11, it must, before being fed into the rectification unit 30 or the high-pressure column 31, be called again to the temperature level discussed above. For this purpose, said fluid stream is now conducted through the cold storage unit 50 or the cold storage means 51 thereof. In this way the cold previously stored in the second operating mode is extracted from the cold storage unit 50 or the cold storage means 51 thereof in the third operating mode.

FIGS. 4A to 4C show the alternative use of a heat storage unit 50 with two heat storage means 51 and 52. The operating modes illustrated in FIGS. 4A to 4C are in this case basically similar to the operating modes illustrated in FIGS. 3A to 3C. However, in the second operating mode, only a part of the fluid stream b1 is conducted through the first cold storage means 51, whereas a second partial stream of the fluid stream b1 is conducted through the second cold storage means 52. Here, the second part of the fluid stream b1 is firstly supplied to the cold side of the main heat exchanger 11, is extracted from the latter at an intermediate temperature level, is conducted through the second cold storage means 52, and is subsequently merged, at an intermediate temperature level, with the first part of the fluid stream b1 in the main heat exchanger 11. A corresponding situation also applies, in the reverse direction, for the third operating mode shown in FIG. 4C. Here, firstly, the fluid stream b2 is supplied entirely to the cold side of the main heat exchanger 11. A part is conducted through the main heat exchanger 11 as far as the hot-side end and is subsequently cooled in the first cold storage means 51. A second part is extracted at an intermediate temperature level, is conducted through the second cold storage means, is subsequently recycled, at an intermediate temperature, into the main heat exchanger 11, and is merged, on the hot side, with the first part of the fluid stream b1.

The corresponding use of two cold storage means in a cold storage unit, and the conducting of fluid streams as discussed above, or similar conducting of fluid streams, serves for improved balancing of the main heat exchanger 11. Said main heat exchanger may basically also be used for the other method variants discussed below, and other embodiments.

FIGS. 5A to 5C illustrate the alternative use of liquid oxygen, or a part of the fluid stream p (ICLOX) for the operation of the cold storage unit 50 of the cold storage means thereof according to an embodiment of the invention. As shown in FIG. 5B with regard to the second operating mode, a part of the fluid stream p (ICLOX) is in this case branched off in the form of a fluid stream p1, is conducted through the cold storage unit 50 or the cold storage means 51 thereof, and is subsequently merged with the rest of the fluid stream p, which is conducted through the main heat exchanger 31. The fraction conducted through the cold storage means 51 is, like the fraction conducted through the cold storage unit 50, evaporated. In the reverse direction, it is the case as per FIG. 5C that, in the third operating mode, the fluid stream p (ICLOX) is firstly entirely heated and evaporated in the main heat exchanger 31. Subsequently, a part is branched off in the form of a fluid stream p2, is cooled and liquefied in the cold storage unit 50 or the cold storage means 51 thereof, and is put into storage in liquid form in the liquid storage unit 40 or in the liquid oxygen store 43.

It is also the case here that, in the second operating mode as per FIG. 5B, as a result of the removal of the oxygen-rich liquid from storage in the liquid oxygen store 43, “excess” cold is available which can be utilized for cooling the cold storage unit 50 or the cold storage means 51 thereof. By way of the stored cold, it is possible, in the third operating mode as per FIG. 5C, for the liquid oxygen store 43 to be refilled. The embodiment as per FIGS. 5A and 5B may also be used with multiple cold storage means, correspondingly to FIGS. 4A to 4C. Other liquids may also be used.

FIGS. 6A to 6C illustrate the use of the so-called impure nitrogen of the fluid stream v (UN2) for the cold storage unit 50 used according to an embodiment of the invention. In the second operating mode of FIG. 2B, a part of a fluid stream v of said type is, as illustrated here in the form of the fluid stream v1, conducted through the cold storage unit 50 or the cold storage means 51 thereof, is heated in the process, and is subsequently merged with the fraction that is heated in the main heat exchanger 11. By contrast, in the third operating mode illustrated in FIG. 6C, the fluid stream v is entirely heated, and a part is subsequently drawn off, in this case in the form of a stream v2, with said part being conducted through the cold storage unit 50 or the cold storage means 51 thereof by way of a blower 53 which is required for maintaining a corresponding fluid stream, and being merged again with the fluid stream v upstream of the main heat exchanger 11.

FIGS. 7A to 7C illustrate the method variants shown in FIGS. 6A to 6C in conjunction with the use of a cold storage unit 50 with multiple cold storage means 51 and 52. The details shown here emerge directly to a person skilled in the art viewing FIGS. 6A to 6C together with FIGS. 4A to 4C and the corresponding explanations.

FIGS. 8A to 8C show, and a modification of the embodiment illustrated in FIGS. 6A to 6C, how an additional passage 11 a in the main heat exchanger 11 can be used. The method variant as per FIG. 8B, that is to say the second operating mode, in this case does not differ significantly from the second operating mode illustrated in FIG. 6B. By contrast, in the third operating mode of FIG. 8C, the impure nitrogen of the fluid stream v2 is, after the cooling in the cold storage unit 50, heated in the main heat exchanger 11 and led out of the plant, for example blown into the surroundings (amb). The embodiment as per FIGS. 8A to 8C may also be used with multiple cold storage means 51, 52.

FIGS. 9A to 9C finally show how the fluid stream c (JT-AIR, see also FIG. 2) can be used for the operation of a corresponding cold storage unit 50. For this purpose, in the second operating mode illustrated in FIG. 9B, a fraction of the air of the fluid stream c is extracted on the cold side of the main heat exchanger 11, as illustrated by way of fluid stream c1, and is conducted through the cold storage unit 50 or the cold storage means 51 thereof. Subsequently, cooling in the main heat exchanger 11 is performed. In the third operating mode as per FIG. 9C, the air is, as illustrated by way of fluid stream c2, firstly heated in the main heat exchanger 11 and subsequently conducted through the cold storage unit 50. 

1. Method for producing an air product in an air separation plant having a heat exchanger unit, an expansion/compression unit, a rectification unit, a liquid storage unit, a cold storage unit and a main air compressor, the method comprising: all of the air supplied to the rectification unit is conducted through the main air compressor and, there, is firstly compressed to a pressure level which lies at least 3 bar above the highest pressure level at which the rectification unit is operated, one or more cryogenic liquids is or are produced in a first production amount in a first operating mode, in a second production amount in a second operating mode and in a third production amount in a third operating mode in the rectification unit using the air conducted through the main air compressor, wherein the second production amount is lower than the first production amount and the third production amount is higher than the first production amount, the one or more cryogenic liquids is or are put into storage in the liquid storage unit in a putting-into-storage amount, which corresponds to a partial amount of the third production amount, in the third operating mode, and said one or more cryogenic liquids is or are removed from storage in the liquid storage unit, in a removing-from-storage amount, in the second operating mode, the one or more cryogenic liquids is or are evaporated and/or pseudo-evaporated in a first evaporation amount in the first operating mode, in a second evaporation amount in the second operating mode and in a third evaporation amount in the third operating mode, wherein the first evaporation amount corresponds to the first production amount, the second evaporation amount corresponds to the second production amount plus the removing-from-storage amount, and the third evaporation amount corresponds to the third production amount minus the putting-into-storage amount, wherein the first, the second and the third evaporation amount differ from one another by no more than 10%, and, using the air conducted through the main air compressor, in the second operating mode, a cryogenic fluid stream is formed, using which the cold storage unit is cooled and which is thereby heated, and in the third operating mode, a hot fluid stream is formed, using which the cold storage unit is heated and which is thereby cooled.
 2. Method according to claim 1, wherein a part of the air conducted through the main air compressor and compressed there is expanded to a pressure level which corresponds at least to the highest pressure level at which the rectification unit is operated, and in which method the cryogenic fluid stream and the hot fluid stream are formed from a part of the expanded air, wherein the part of the expanded air for forming the cryogenic fluid stream is, after the expansion, conducted unheated through the cold storage unit and is heated in the heat exchanger unit to form the hot fluid stream and is subsequently conducted through the cold storage unit, and/or a rectification unit with a high-pressure column and a low-pressure column is used, wherein a gas mixture which comprises a nitrogen content of 0.5 to 5 mole percent is extracted from the low-pressure column, and in which method the cryogenic fluid stream and the hot fluid stream are formed from a part of the gas mixture extracted from the low-pressure column, wherein said part is used unheated to form the cryogenic fluid stream and is heated in the heat exchanger unit to form the hot fluid stream, and/or a further part of the air conducted through the main air compressor and compressed there is subsequently compressed further and cooled in the heat exchanger unit, and in which method the cryogenic fluid stream and the hot fluid stream are formed from a part of the further compressed air that has been cooled in the heat exchanger unit, wherein said part is used unheated to form the cryogenic fluid stream and is heated in the heat exchanger unit to form the hot fluid stream.
 3. Method according to claim 1, in which method the cryogenic fluid stream is formed from a part of the one or more cryogenic liquids that is or are evaporated or pseudo-evaporated in the second operating mode, before the evaporation thereof, and in which method the hot fluid stream is formed from a part of the one or more cryogenic liquids that is or are evaporated or pseudo-evaporated in the third operating mode, after the evaporation thereof.
 4. Method according to claim 2, in which a part of the hot fluid stream, after the cooling thereof in the cold storage unit, is heated in the heat exchanger unit.
 5. Method according to claim 1, in which the cold storage unit has first cold storage means and second cold storage means, wherein in each case a first part of the cryogenic fluid stream and of the hot fluid stream is conducted through the first cold storage means, and a second part is conducted through the second cold storage means.
 6. Method according to claim 5, in which the second part of the hot fluid stream and of the cryogenic fluid stream is conducted in each case through a section of a main heat exchanger of the heat exchanger unit before and/or after being conducted through the second cold storage means.
 7. Method according to claim 1, in which the one or more cryogenic liquids comprise(s) a nitrogen-rich and/or an argon-rich and/or an oxygen-rich liquid and/or liquid air.
 8. Air separation plant having a heat exchanger unit, comprising an expansion/compression unit, a rectification unit, a liquid storage unit, a cold storage unit and a main air compressor, which air separation plant has means which are designed to conduct all of the air supplied to the rectification unit through the main air compressor and, there, to firstly compress said air to a pressure level which lies at least 3 bar above the highest pressure level at which the rectification unit is operated, to produce one or more cryogenic liquids in a first production amount in a first operating mode, in a second production amount in a second operating mode and in a third production amount in a third operating mode in the rectification unit using the air conducted through the main air compressor, wherein the second production amount is lower than the first production amount and the third production amount is higher than the first production amount, to put the one or more cryogenic liquids into storage in the liquid storage unit in a putting-into-storage amount, which corresponds to a partial amount of the third production amount, in the third operating mode, and to remove said one or more cryogenic liquids from storage in the liquid storage unit, in a removing-from-storage amount, in the second operating mode, to evaporate and/or pseudo-evaporate the one or more cryogenic liquids in a first evaporation amount in the first operating mode, in a second evaporation amount in the second operating mode and in a third evaporation amount in the third operating mode, wherein the first evaporation amount corresponds to the first production amount, the second evaporation amount corresponds to the second production amount plus the removing-from-storage amount, and the third evaporation amount corresponds to the third production amount minus the putting-into-storage amount, wherein the first, the second and the third evaporation amount differ from one another by no more than 10%, and, using the air conducted through the main air compressor, to form, in the second operating mode, a cryogenic fluid stream using which the cold storage unit is cooled and which is thereby heated, and to form, in the third operating mode, a hot fluid stream using which the cold storage unit is heated and which is thereby cooled. 